1. Field of the Invention
The present invention relates to a zoom-type image forming apparatus capable of forming a magnification-varied image.
2. Description of the Related Art
In general, this type of image forming apparatus, e.g. a zoom copying machine, has an exposure optical system comprising a lens for forming an image of an original on an image carrying body, a mirror, etc.
The lateral magnification (i.e. a magnification in a direction perpendicular to the direction in which a paper sheet is moved) is varied by moving the lens and varying the length of an optical path. The focus is adjusted by moving the mirror.
In the equal-size copy mode (magnification=100%), the following equation is generally given: EQU a:(c-a)=2f:2f
where a=the distance between face A of an original and lens L,
c=the distance between face A of an original and face B of a photosensitive drum functioning as an image carrying body, and PA1 f=the focal distance of a lens. PA1 means for inputting data for setting an image formation magnification, data for adjusting the lateral magnification, and data for adjusting focus; PA1 means for moving the optical devices on the basis of the data input by the input means; PA1 means for inputting position data on the optical devices when a first magnification and a second magnification are input by the input means, the optical devices are moved by the moving means, and the lateral magnification and the focus are adjusted; PA1 memory means for storing the position data input by the position data inputting means; and PA1 means for calculating a coefficient for correcting a difference in optical path length due to a variation in characteristics, of the optical devices on the basis of the position data stored in the memory means, and calculating the positions of the optical devices by substituting the coefficient when the image formation magnification is input by the input means. PA1 means for inputting data for setting an image formation magnification, data for adjusting the lateral magnification, and data for adjusting focus; PA1 means for moving the lens on the basis of the data input by the input means; PA1 means for moving the mirror on the basis of the data input by the input means; PA1 means for inputting position data on the lens and the mirror when a minimum reduction magnification and a maximum enlargement magnification are input by the input means, the lens and the mirror are moved by the moving means, and the lateral magnification and the focus are adjusted; PA1 memory means for storing the position data input by the position data inputting means; PA1 means for calculating a coefficient for correcting a difference in optical path length due to a variation in characteristics of the lens, on the basis of the position data stored in the memory means, and calculating the positions of the lens and the mirror by substituting the coefficient when the image formation magnification is input by the input means; and PA1 means for controlling the lens moving means to move the lens to the position calculated by the calculating means and, controlling the mirror moving means to move the mirror to the position calculated by the calculating means.
In the 50% magnification copy mode, the following is given: EQU a:(c-a)=3f:1.5f
In the 200% magnification copy mode, the following is given: EQU a:(c-a)=1.5f:3f
These equations are established in the ideal state in which a variation of lens need not be corrected.
The distances a and c (including correction values) are expressed by EQU a=2f+K1 (1/m-1)(1+.alpha.) EQU c=4f+K2 (m+1/m-2)(1+.alpha.) EQU K1, K2=the constants given by the lens, EQU m=magnification (0.5-2.0), and EQU .alpha.=the coefficient for correcting a variation of lenses.
In a conventional image forming apparatus of this type, the values of .alpha. are stored in the form of codes representing lens types selected from among predetermined 21 lens types.
When the lateral magnification of copy and focus are adjusted, the adjustment mode is set in the apparatus. The adjustment of 100% lateral magnification (lens position adjustment) and the focus adjustment (position adjustment of a third carriage having the mirror) are performed, while the copied image is viewed. In the zoom mode, the optimal lens position at which, e.g. 50% or 200% lateral magnification adjustment and focus adjustment are achieved, is found, and the pulse motor drive data for shifting the lens to the optical lens position is input and memorized. By accessing the drive data, the lens and mirror are driven in an interlocking manner.
In this conventional method, however, one must perform actual copying operations several times and check the copied images, thereby finding the optimal drive data. In addition, since the lens and mirror are driven in an interlocking manner, there may occur an undesirable situation in which the focus is not adjusted although the lateral magnification is adjusted, or the lateral magnification is not adjusted although the focus is adjusted, or both the lateral magnification and focus are not adjusted.
Moreover, in the conventional method, a mechanical error cannot be corrected.
As has been stated above, in the conventional zoom-type image forming apparatus, it is troublesome to obtain optimal drive data for adjusting the lateral magnification and focus, and the obtained data is not satisfactory.